Iontophoretic drug delivery systems, have, in recent years, become an increasingly important means of administering drugs.
Presently there are two types of transdermal drug delivery systems, i.e., passive and iontophoretic. Passive patch systems deliver small and relatively lipophilic drugs through the skin of the patient by diffusion, an example of which would involve the application of a narcotic analgesic patch to provide pain relief. Iontophoresis systems, on the other hand, deliver drug through the skin of the patient through the application of an electromotive force (iontophoresis) to drive ionizable substances (medicament) into the skin so that they can be absorbed by adjacent tissues and blood vessels. Iontophoresis, therefore, allows charged and hydrophilic drugs to be transported across the skin which are poorly deliverable through passive diffusion. Transdermal systems offer advantages clearly not achievable by other modes of administration, such as hypodermic injection which has the associated problem of pain, risk of infection and trauma to the patient. Iontophoresis also has advantages over oral administration in that introduction of the drug through the gastrointestinal tract may result in inactivation of the medicament, food interactions, first pass hepatic metabolism and gastrointestinal side effects.
Conventional iontophoretic devices, such as those described in U.S. Pat. No. 4,820,263 (Spevak, et al.), U.S. Pat. No. 4,927,408 (Haak, et al.) and U.S. Pat. No. 5,084,008 (Phipps), the disclosures of which are hereby incorporated by reference, provide for delivery of a drug or medicament transdermally through iontophoresis. Basically, conventional iontophoretic devices consist of a power source connected to two electrodes, an anode and a cathode, which are individually in ionic contact with an electrolyte or drug reservoir which is in contact with the skin to be treated by the iontophoretic device. When the current is turned on, electrical energy is used to assist in the transport of ionic molecules into the body through the skin, via ionic conduction.
In the recent past, electrically conductive printed traces have been used within an iontophoretic device to make the necessary electrical connections. Conductive adhesives were used for making the electrical connection. The adhesives used for electronic interconnection bonding known in the art prior to the present invention, was comprised of epoxy and pressure sensitive adhesives. The starting points for making epoxy adhesives are fliud viscous low molecular prepolymer materials obtained either as single component or two component compositions. In the prior art where a conductive additive filler is used, the filler must be incorporated before curing occurs. The additiion of a conductive filler will increase the viscosity of the prepolymer and if the filler concentration is too high, the epoxy prepolymer-filler mix will be difficult if not impossible to apply. Therefore the selection of the filler is limited to the most highly conducting and coincidentally, the expensive materials, e.g. silver powder, and even thenit may not be possible to incorporate sufficient conducting filler to accomplish its purpose. Once the conductive filler epoxy is formed and cured, the epoxy is irreversibly cured and is cannot be used in remelting and resealing operations. It is incapable of bonding to a new surface and therefore could not be used in assembly of a device with the conductive adhesive in dry form mostly because once dried or cured it cannot be remelted or recured. Further disadvantages of epoxies in addition to the high cost, are slow curing time, toxcity of the prepolymers and possible vapor release or outgassing during curing, they could not be used in high speed manufacturing due to long cure times and due to their liquid form there were problems with using conventional coating techniques.
Pressure sensitive adhesives are applied in thin layers which produce weak bonds especially when attempting to bond to a metal mesh. Costs are high and efficiency of the conductive component is low resulting in poor electrical conductivity. Prior art pressure sensitive adhesives also had other manufacturing and application problems. For example, due to the tendency of pressure sensitive adhesives to retain solvent they resulted in outgassing during preparation and use.
These difficulties and shortcomings have led Applicants to the present invention which overcomes these difficulties and shortcomings.